Growth, Characterization, and Properties of Epitaxial Metal/Nitride Superlattices

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The aim of this research is to investigate strengthening mechanisms in deposited epitaxial single-crystal nitride/metal superlattices where the layers have different slip systems. Materials systems are NbN/Mo, NbN/W, VN/Cr, AlN/Mo, and AlN/W, providing both cubic-B1/cubic-BCC and hexagonal-wurtzite/cubic-BCC combinations. Both (001) and (111) oriented MgO and W substrates are used. It will be determined if AlN can be grown in a cubic structure when surrounded with cubic (001) layers. These materials should exhibit large strength and hardness enhancements due to the superlattice structure. Correlations between layer characteristics, strength, and hardness will provide new information on strengthening mechanisms. Changes in the layer lattice mismatch (in superlattices containing alloy VN-NbN or Cr-Mo layers) are used to produce superlattices with both coherent and incoherent interfaces. Unlike previously-studied nitride/nitride superlattices, these layers are immiscible such that the structures are stable and retain their desirable characteristics at high temperatures. Structure a nd property studies versus annealing time and temperature are carried out, and the results compared with results from nitride/nitride superlattices. %%% There is technological interest in nitride/nitride superlattices where early results show dramatic improvements over conventional nitride coatings in cutting tools.